Mercer County is a county in Illinois. It covers 569 square miles (364,102 acres), which represents less than one percent of the state total. Of the 102 counties in Illinois, Mercer County ranks 72nd in terms of the size of its population (15,858, according to 2015 Census estimates). Recent Lands of America data places the average value of ranches, land, farms and other recreational acreage for sale in Mercer County at $4,150 per acre. The average list price of property and land for sale was $209,160 and the median size of land and real estate for sale in Mercer County was 50 acres. Land for sale in Mercer County totaled 50 acres and $209,160 in overall land value, with the city of Keithsburg featuring the most land for sale in the county. Farmland was the most common type of land for sale in Mercer County.